Known medical imaging techniques comprise, on the one hand, nuclear medical techniques which mainly image functional processes in an examination object, and, on the other hand, techniques, such as magnetic resonance imaging or computed tomography techniques, which predominantly image examined anatomy.
The PET (positron emission tomography) technique is a nuclear medical imaging technique. PET generates images of living organisms by visualizing the distribution in the organism of a previously dispensed, weakly radioactively marked substance (radiopharmaceutical) which was enriched in the organism such that biochemical and physiological processes can be imaged.
Radionuclides, which emit positrons during decay, are suitable radiopharmaceuticals for this process. After a short distance (approximately 2-3 mm), the positrons interact with an electron and this results in so-called annihilation. In the process, both particles—positron and electron—are destroyed and two high-energy photons (gamma radiation) of 511 keV each are created and travel apart from each other at an angle of approximately 180°. The line formed in the process is also referred to as the line of response (LOR). The two photons (annihilation radiation) are measured at e.g. a detector ring on which they impinge simultaneously at two locations. As a result of the coincidence of the two measurement results, the positron emission can be verified and it is possible to estimate the location of the annihilation.
The magnetic resonance imaging technique (in the following text, MRI is an abbreviation of magnetic resonance imaging) is a known technique by means of which images of the interior of an examination object can be generated. In simplified terms, the examination object is to this end positioned, in a piece of MRI equipment, in a comparatively strong static, homogeneous basic magnetic field (field strengths between 0.2 Tesla and 7 Tesla and higher) so that the nuclear spins of the examination object are aligned along the basic magnetic field. In order to effect nuclear magnetic resonances, radiofrequency excitation pulses are radiated into the examination object, the effected nuclear magnetic resonances are measured and MRI images are reconstructed on the basis thereof. Rapidly switching magnetic gradient fields are superposed on the basic magnetic field in order to encode spatial information in the measurement data. The recorded measurement data is digitized and stored as complex numerical values in a k-space matrix. The k-space matrix filled with values can be used to reconstruct an associated MRI image by means of a multi-dimensional Fourier transform. This technique permits an excellent display of soft parts in particular with selectable contrasts.
There are attempts to combine MRI and PET systems in order to synergistically utilize the advantages of both techniques. The laid-open patent application US 2007/0102641 A1 describes one example of a combined PET/MRI system.
When combining the different systems, the emphasis predominantly until now was on matching the respectively specific measurement units, such as a magnetic unit of the MRI system and a detector unit of the PET system. However, other components required for examining a patient can also affect the quality and capability of such a combined PET/MRI system.
DE 10 2006 037 047 A1 discloses a detection unit comprising a PET detector arrangement and a radiofrequency coil arrangement in which the longitudinal conductors of the radiofrequency coil arrangement are guided, in sections, along intermediate spaces between mutually spaced-apart detector blocks of the PET detector arrangement.
US 2005/0284490 A1 discloses a method and an apparatus for registering and immobilizing a patient. A neck support provided for immobilization is composed of materials which are compatible with X-ray images, magnetic resonance imaging and positron emission tomography.
DE 197 31 234 A1 relates to a patient bearing apparatus which is compatible with both X-ray and magnetic resonance imaging examinations.